The present invention relates generally to a speaker microphone assembly for use with a communication device, and more particularly, relates to a remote speaker microphone (RSM) for use with a two-way radio.
Referring to FIG. 1, an RSM 100, according to the prior art, typically includes a housing 101 that carries a microphone 102 mounted within the housing and positioned facing outwardly from the front of the housing. A Push-To-Talk (“PTT”) button 104 is mounted to the left side of the housing. A speaker 105 is mounted within the housing and positioned facing outwardly through the front of the housing. A louvered or shutter opening area 103 may be formed in the housing directly in front of speaker 105. A cable 106 extends downwardly from housing 101 to interconnect the RSM with a communication device (not shown) such as a two-way radio.
A directional microphone may be used in such an RSM and would utilize front and rear ports in the housing and serve to sense the difference between the instantaneous air pressures, which impinge on two diaphragm surfaces of the directional microphone. An internal delay at the rear port to a diaphragm surface is optimally designed to time and cancel the distance delay, thus allowing unwanted sound to reach the diaphragms from both ports simultaneously and therefore be cancelled.
The directional microphones that are typically used in RSMs are relatively small in comparison to the front-to-back thickness of the speakers that are used in RSMs. For example, a typical directional microphone element may be in the order of about 6 mm in diameter and about 5 mm thick (front to back). A typical RSM housing, on the other hand, may be on the order of about 25 mm thick (front to back). In known RSM devices, the housing size in general, and it's front-to-back thickness (i.e., its depth) in particular, is determined as a function of the size of the components positioned within the housing, as for example, a speaker, a printed circuit board (“PCB”), a PTT switch, an earphone jack, and any other internal components. Due to the physical size (or geometry) of the housing in relation to the directional microphone, known RSM devices include relatively large channels (cavities, or chambers) at the front and rear of the directional microphone.
For example, FIG. 2 illustrates a prior art mounting of a directional microphone 108 in an RSM housing 101. As shown in FIG. 2, directional microphone 108 is generally positioned midway between front and rear walls 110, 118 of RSM housing 101. A front channel 124 extends between a front port 112 of housing 101 and a front surface 114 of microphone 108. Likewise, a rear channel 126 extends between a rear port 116 of the housing and a rear wall 120 of microphone 108. However, due to the relatively small size of the microphone (e.g., thickness from front surface 114 to back surface 120) in comparison to the thickness of the housing (from front wall 110 to rear wall 118), the rear surface 120 of the microphone 108 is laterally spaced from the housing's rear wall 118 and rear port 116. As a result, sound waves passing through rear port 116 must travel through rear channel 126 (which is a cavity or chamber) in housing 101 before reaching rear surface 120 of microphone 108. The acoustic effect of channels, cavities, and chambers, such as those shown in FIG. 2, may significantly degrade the noise reduction properties of a directional microphone.